1. Field of the Invention
The present invention relates to apparatuses and methods for reading images, which are suitable for use in image-reading scanners. The invention also relates to computer-readable storage mediums storing image-processing programs.
2. Description of the Related Art
In general, a scanner includes a lamp having a fixed illumination intensity, by which a CCD is not saturated. In this case, the illumination intensity of the lamp, which can prevent the CCD from saturating, is set in such manner that only the lower part of the linear region in a photoelectric conversion range of the CCD is used in consideration for variations in luminance of the lamp. In this case, however, when the luminance of the lamp is smaller than an average, the level of a CCD output signal becomes extremely small. As a result, compensation for decrease in the CCD signal level must be made by increasing an analog gain of the CCD output signal. This leads to degradation of the S/N ratio of a scanned image.
In order to avoid this problem, it is necessary to utilize the linear region in the CCD photoelectric conversion range as much as possible. In this case, according to changes in the variations of CCD sensitivity and changes in one of the transmittance and the reflectance of an original to be scanned, the illumination intensity of the lamp needs to be adjustable over a wide range. However, when a fluorescent tube having a high luminance is used as a light source to be adapted to a negative film which has a wide latitude, it is difficult to change the illumination intensity of the lamp in a wide range and stable condition.
In addition, before inserting the original to be scanned, it is not possible to adjust the illumination intensity to the entire linear region of the CCD photoelectric conversion range while including the transmittance of the original, since saturation of the CCD and saturation of an analog gain of the CCD output signal occur.
As mentioned above, in the conventional scanner having the fixed luminance of the light source, due to the saturation of the CCD, the variations in the CCD sensitivity, and the variations in the light-source luminance, it is necessary to set a low-level illumination intensity with respect to the saturation voltage of the CCD. Therefore, it is difficult to effectively utilize the CDD photoelectric conversion range. As a result, since the CCD output level decreases, in contrast, the analog gain increases to form an image signal. Thus, a satisfactory S/N ratio is difficult to obtain.
In addition, when the scanner performs a self-compensation by controlling the aforementioned analog gain, it is impossible to obtain an analog gain appropriate to adjust a gray balance at a reading time in case the CCD reaches the saturation region.
Accordingly, in order to solve the above problems, it is an object of the present invention to provide an apparatus and a method for reading an image, and a computer-readable storage medium, in which the photoelectric conversion region of a CCD can effectively be used and the gray balance of individual red, green, and blue color (RGB) signals can be maintained.
According to a first aspect of the present invention, there is provided an image reading apparatus. This apparatus includes a light-source unit for illuminating an original to be read and a photoelectric conversion unit for reading light from the original to convert the light into an image signal. An illumination-intensity controlling unit controls the illumination intensity of the light-source unit. A setting unit sets an electric-charge storage time of the photoelectric conversion unit in a manner that the photoelectric conversion unit is not saturated in a state in which the illumination intensity of the light-source unit is maximized by the illumination-intensity controlling unit. A first determining unit determines the illumination intensity of the light-source unit by controlling the illumination-intensity controlling unit in a state in which the photoelectric conversion unit directly reads the light of the light-source unit after setting of the electric-charge storage time by the setting unit.
According to a second aspect of the present invention, there is provided an image reading apparatus. The apparatus includes a photoelectric conversion unit that reads light from an original to convert the light into an image signal. An amplifying unit amplifies the image signal output from the photoelectric conversion unit. A setting unit sets an electric-charge storage time of the photoelectric conversion unit to be shorter than the storage time set at the time of reading of the original. A determining unit determines an amplification factor of the amplifying unit according to the level of the image signal amplified by the amplified unit after setting of the electric-charge storage time by the setting unit.
According to a third aspect of the present invention, there is provided an image reading method, in which a light-source unit illuminates an original and a photoelectric conversion unit reads light from the original to convert the light into an image signal. The image reading method includes the steps of controlling the illumination intensity of the light-source unit in such a manner to be maximized, setting an electric-charge storage time of the photoelectric conversion unit in a manner that the photoelectric conversion unit is not saturated in a state in which the illumination intensity is maximized, and determining the illumination intensity of the light-source unit in a state in which the photoelectric conversion unit directly reads the light of the light-source unit after the setting.
According to a fourth aspect of the present invention, there is provided an image reading method, in which a photoelectric conversion unit reads light from an original to convert the light into an image signal. The image reading method includes the steps of amplifying the image signal output from the photoelectric conversion unit, setting an electric-charge storage time of the photoelectric conversion unit to be shorter than the storage time set at the time of reading of the original, and determining an amplification factor of the amplifying step according to the level of the amplified image signal after the setting step.
In addition, according to a fifth aspect of the present invention, there is provided a computer-readable storage medium storing a processing program. This program includes the steps of illuminating an original by a light-source unit, reading light from the original to convert the light into an image signal by a photoelectric conversion unit, controlling the illumination intensity of the light-source unit in such a manner to be maximized, setting an electric-charge storage time of the photoelectric conversion unit in a manner that the photoelectric conversion unit is not saturated in a state in which the illumination intensity is maximized, and determining the illumination intensity of the light-source unit by controlling the illumination intensity in a state in which the photoelectric conversion unit directly reads the light of the light-source unit after the setting.
In addition, according to a sixth aspect of the present invention, there is provided a computer-readable storage medium storing a processing program. The program includes the steps of reading light from an original by a photoelectric conversion unit to convert the light into an image signal, amplifying the image signal, setting an electric-charge storage time of the photoelectric conversion unit to be shorter than the storage-time at the time of reading of the original, and determining an amplification factor used in the amplifying processing according to the level of the image signal after the setting.
With the above-described arrangements, the apparatus and the method for reading an image, and the computer-readable storage medium can be provided in which the CCD photoelectric conversion region can effectively be used and gray balance of the RGB color signals can be adjusted.